1. Field of the Invention
The present invention relates in general to air conditioners, and relates in particular to an air conditioning system having a continuous air processing capability by alternately treating the process air through at least two units of desiccants.
2. Description of the Related Art
FIG. 7 shows a prior art example of desiccant assisted air conditioning system same as the system disclosed in a U.S. Pat. No. 4,430,864. The system comprises: a process air passage A; a regeneration air passage B; two desiccant beds 103A, 103B; and a heat pump device 200 for desiccant regeneration and cooling of process air. The heat pump device 200 utilizes heat exchangers, embedded in the two desiccant beds 103A and 103B, as high and low temperature heat sources. In each of the thermal medium passages, there are opposingly disposed expansion valves 240A, 240B and one-way valves 241A, 241B, which are arranged parallel to the expansion valves 240A, 240B respectively, and the direction of compression of the compressor 230 can be switched by a four-way valve 250.
In the technology described above, cooling and dehumidifying processes can be explained with reference to a psychrometric chart shown in FIG. 8. The process air (state K) is withdrawn by a blower 102 through a passage 110, raised in pressure, and is forwarded to the one desiccant bed 103A through the passage 111 and the four-way valve 105 and passage 112A, where the moisture in the process air is adsorbed, to lower its humidity ratio and raise its temperature by the effect of the heat of adsorption. Because the desiccant bed 103A is cooled by the heat pump 200 through the heat exchanger 220, the adsorption heat is absorbed and the temperature of the process air does not rise too much, and after satulating (state L), the process air is dehumidified along iso-relative humidity line. The process air which has been dehumidified and maintained at a temperature (state N) is supplied to the conditioning space through the passage 113A, the four-way valve 106, passage 114. An enthalpy difference DQ is thus produced between the return air from the conditioning space (state K) and the cooled process air (state N), to provide cooling of the conditioning space. The regeneration process of the desiccant is performed as follows. Regeneration air (state Q) is withdrawn into the blower 140 through the passage 120, raised in pressure, and is forwarded to the other desiccant bed 103B through the passages 121, 122, the four-way valve 106, and the passage 113B. The desiccant bed 103B is heated by the heat pump 200 by way of the heat exchanger 210, so its temperature is raised, and the relative humidity is lowered (state R). The regeneration air which now has a lowered relative humidity passes through the desiccant bed 103B to remove the moisture from the desiccant material (state T). The regeneration air which has passed through the desiccant bed 103B passes through the passage 112B, four-way valve 105 and the passage 124 and is discharged to an outside environment.
After the air conditioning process has been carried out for sometime and the moisture content in the desiccant becomes higher than a certain value, the four-way valve is operated to be switched, so that the air passages for the desiccants and cooling/heating of the heat pumps are interchanged. Thus, the operation is carried on so that the regenerated desiccant is used to continue air conditioning operation while the other desiccant is being regenerated. Therefore, it can be seen that the processes of adsorption and regeneration are conducted in a batch type system.
In the technology described above, heat exchange of the low temperature heat source of the heat pump and the desiccant for adsorption are embedded into a unit, and heat exchange of the high temperature heat source of the heat pump and the desiccant on the regeneration side are embedded into a unit. So, the cooling effect DQ is provided by a direct thermal load on the heat pump (refrigeration device), which means that it is not possible to generate more cooling than that allowed by the capacity of the heat pump acting as a refrigeration device. Therefore, this configuration does not provide any advantages worthy of making the apparatus complex.